The present invention refers to a method for rolling a continuous billet fed from a billet-heating furnace set upstream of a roll train, of the type in which, between the furnace and the first stand of the roll train, welding is envisaged, in moving conditions, of the head of each billet sent out of the furnace to the tail of the continuous billet being rolled.
The invention also refers to a plant which is particularly suitable for the implementation of said method.
The persons skilled in the branch are well acquainted with the methods for rolling a continuous billet that has come out of a billet-heating furnace which is aligned with a roll train.
All the aforesaid methods set themselves the same aim, namely that of increasing productivity of the rolling mill, at the same time obtaining a high-quality final product.
Methods for rolling a continuous billet of the type generically indicated above are, for instance, described in the patents EP-0761330 and EP-0832700, to which the reader is referred if further clarifications were necessary.
In brief, EP-0,761,330 regards a continuous rolling method comprising the steps of: moving simultaneously a mobile flash butt-welding machine and a deburring machine, which can be moved separately during welding; carrying out butt welding while the welding machine and the deburring machine are moving along a pre-set welding path; moving the deburring machine backwards together with the welding machine to meet the welded part, and bringing the welding machine backwards into a waiting position, after completion of welding; and removing the burrs from the welded part while the deburring machine is changing the direction of its travel and is moving according to a specific path after the welded part has reached a pre-determined position.
EP-0,761,330 also refers to a plant for implementation of the method described above, comprising: a rotary table which connects the axis of a continuous casting upstream to a rolling axis downstream, and which transfers the billets that have come out of the furnace upstream of the rotary table along the rolling axis; a descaling device for removing the scale from the billets; a mobile flash butt-welding machine which continuously joins a rear end (tail) of the previous billet to a front end (head) of the subsequent billet by means of flash butt-welding; a mobile deburring device which removes the burrs from the welded part of the billets by means of a grinder; and an induction heater which heats a continuously joined billet. EP-0,832,700 regards both a process for welding billets coming out of a furnace, and a plant for rolling billets that adopts the said welding process.
More precisely, EP-0,832,700 described a welding process for billets coming out of a heating furnace along an axis coinciding with the rolling axis, where, in the stretch between the heating furnace and the first rolling stand, a precise layout of operating units is envisaged. The following are in fact provided: at least one feeding device, a roller way for conveying billets, a mobile welding unit equipped with welding yokes, and an emergency billet shear.
In one first step of the process, the tail of the billet being rolled is welded to the head of the billet that has come out of the furnace, and this welding operation is carried out on the two billets, while these are moving, by a welding unit, which is mounted on a mobile trolley.
According to the invention that forms the subject of EP-0,832,700, the mobile trolley, which carries the welding unit, in one first stationary waiting condition, provides for the two ends of the billets to be joined coming into contact; next, the trolley, as it advances, accelerates to the rolling speed, and in this condition welding of the. ends of the billets takes place. Finally, there is a backing-off step in which the trolley returns to the starting position.
A further characteristic of the process according to EP-0,832,700 regards welding of the ends of the billets, which is preceded by a descaling step and a shearing step, while the billets are moving, in which the two ends of the billets set against one another for welding are sheared. The latter step is carried out by means of a shearing unit set on board the mobile trolley, upstream of the welding unit.
Another characteristic is that the welding step is followed by a deburring step, also performed in moving conditions by a deburring machine unit.
Processes and plants for welding billets are described and illustrated also in the patents DE 28 36 338 and U.S. Pat. No. 2,214,618.
DE 28 36 338 refers to a welding process in which a mobile trolley is present that follows the billets to be joined, before the subsequent processing.
According to the two embodiments that are illustrated in the above patent, the mobile trolley may be placed either directly downstream of the furnace, or immediately upstream of the rolling stands.
DE 28 36 338 does not provide any indication as regards treatment of the ends of the billets that are to be welded together.
U.S. Pat No. 2,214,618 (which regards the welding of coils) envisages a trolley carrying a shearing element, a welding element, and a grinding element for grinding the portion welded. In addition, it is specified that welding between the tail of the strip of the first coil and the head of the strip of the second coil is carried out in moving conditions, without stopping the rolling plant.
The general purpose of the present invention is to propose a method and corresponding plant for rolling a continuous billetxe2x80x94formed by mutual welding of a plurality of billets that have come out of a billet-heating furnacexe2x80x94which will ensure advantages with respect to the known methods.
The above purpose is achieved by a method and plant having the characteristics specified in the attached claims.